The invention relates to handover in wireless telecommunication systems, particularly to changing a radio access gateway between an IP (Internet Protocol) network and a wireless network.
Transferring date associated with various time-critical applications in IP-based networks has been an attractive topic in recent years. An important field of application is Voice over IP (VoIP), i.e. voice transfer utilizing an IP protocol. An H.323 is a standard specified by the International Telecommunication Union (ITU) for packing voice and video image used in video conference programs and for call control. The H.323 standard specifies packet-based transfer of multimedia streams (audio, video, data) in systems that do not necessarily guarantee quality of service (QoS). The H.323 standard is applicable to any IP (Internet Protocol) based network, such as the Internet. H.323 devices can be used both for point-to-point calls and various point-to-multipoint applications. The H.323 is part of a larger collection of standards, i.e. H.32X series standards, which specifies various conference standards for different network types. The H.323 is designed to be compatible with all H.32X standards.
Another standard used for transferring VoIP is a Session Initiation Protocol (SIP), which is a control protocol on the application level developed by the Internet Engineering Task Force (IETF). H.248/Megaco, a standard common to the ITU and IETF for gateways, may also be used in transferring VoIP.
Wireless telecommunication systems utilize radio access gateways (RAGW), which transmit data between a circuit-switched wireless network and an end point in a packet-switched IP network based on an IP protocol. A plurality of base stations controlled by a radio access gateway is typically connected to the radio access gateways. The wireless network can be, for example, a network according to the GSM standard. A radio access network is thus a general term for a device which performs a protocol conversion on the data transmitted between the protocol used in a wireless network and the protocol used in an IP network. The radio access gateways are used particularly for providing wireless connections in different office environments wherein the radio access gateways enable a company local area network and a mobile communication network to be connected. It is to be noted that hereinafter, data transfer may refer to transferring any one or more types of media (audio, video, data). In connection with the present application, the term data is thus used to generally refer to any information regardless of the type thereof.
Current IP-based standards used for transferring audio or video do not as such support handover for an active connection of a terminal. In connection with the present application, the term handover refers to changing a radio traffic channel and radio traffic responsibility from a source system to a target system such that a data transmission connection is maintained for a user's service. Handover may take place because the terminal moves or for other reasons, such as for balancing the load between cells. The radio access gateways are typically connected to, i.e. they are associated with, one or more base stations, and the radio access gateway performs a protocol conversion on the data associated with the terminals served by the base stations. If handover is needed to a base station which is connected to a different radio access gateway, the radio access gateway used must also be changed.
Since each radio access gateway is typically provided with a unique IP address of its own, changing the radio access gateway used would also require the IP address to be changed at the end point in the IP network. This could be carried out by directing the media streams from the end point in the IP network to a new radio access gateway and by excluding the old radio access gateway from connection provision. A major problem with supporting mobility in the devices used for VoIP is that they do not support redirection of media streams at all, or they certainly do not support fast redirection. Consequently, during an active connection, another end point in the IP network cannot be configured to use a new radio access gateway without the quality of service (e.g. speech quality) degrading significantly.